Signal transduction is an important biological process by which information from extracellular stimuli is communicated to cells, resulting in changes in cellular physiology. The long-term objective of this proposal is a description at the molecular level of the mechanisms involved in transmission of the signal generated by pheromone in the yeast mating response. Yeast genetics will be used to elucidate the roles of genes thought to be involved in this process and to identify new genes through suppressor analysis. Haploid yeast cells respond to mating pheromones via two cell type- specific receptors linked to a heterotrimeric G protein. In yeast, unlike most other systems, the betagamma complex of the G protein appears to propagate the signal after release from the alpha subunit due to interaction with occupied receptor. The molecular events that take place downstream of the G protein are not well understood and constitute an important area for study. A specific aim of this proposal is to investigate the function of a gene that was isolated as a multicopy suppressor of a temperature sensitive Gbeta subunit, as well as the function of a closely-related gene. These genes form an essential redundant set because one or the other of them is required for cell viability. Analysis of the expression of these genes and of the defect that occurs when they are not transcribed will be undertaken. Constructs containing an inducible version of each gene will be created for this purpose and will also be used to isolate suppressors that overcome the lethality caused by the lack of both gene products. Alleles of the suppressor gene that are specifically defective in mating will be isolated as well. A second aim is to identify proteins that interact with the Gbeta subunits, a genetic technique for the isolation of interacting gene products. A final aim is the characterization of a receptor-mediated desensitization pathway that blocks transmission of the signal downstream of the Galpha subunit. Mutations will be isolated both in regions of the receptor gene that are involved in this function and in other genes that act downstream in the desensitization pathway. Information gained from these studies will provide insights into mammalian G protein-mediated signalling pathways which control the response to a number of diverse stimuli, including hormones, neurotransmitters, catecholamines, and light.